This application claims priority to an application entitled xe2x80x9cMethod for Transmitting Power Control Signal in Mobile Communication Systemxe2x80x9d filed in the Korean Industrial Property Office on Jul. 7, 1998 and assigned Serial No. 98-27737, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a power control method in a CDMA (Code Division Multiple Access) mobile communication system, and more particularly, to a method for controlling the transmitting power of a forward link.
2. Description of the Related Art
Mobile communication systems perform power control in order to increase or decrease power of a transmission signal according to the condition of a radio link. To control the signal power transmitted from a base station, a closed loop method has been used. In this method, a mobile station measures the receiving power, compares it with a threshold value and informs the base station of the compared result by use of a power control bit on a reverse channel. Then, the base station increases or decreases transmission power by a prescribed step according to the value of the power control bit.
Such power control is performed once every time unit, whereby the time unit is known as a Power Control Group (PCG). The method of power control is as follows. If the base station transmits a signal, the mobile station receives the signal and measures the power of the received signal. The mobile station compares the measured value with a threshold value, generates a power control bit according to the compared result, and transmits the power control bit to the base station. The base station then reads the value of the power control bit and raises or lowers transmission power for the next power control group.
FIG. 1 illustrates a base station and a mobile station, for controlling the power of a forward link. The base station transmits at least one forward signal through a radio link directed to the mobile station. The mobile station transmits a signal including a reverse pilot signal through a radio link directed to the base station.
In a configuration of the base station, a baseband modulator 111 modulates transmission data. A gain multiplier 113 multiplies an output of the modulator 111 by a gain. An RF (Radio Frequency) modulator 115 modulates the output of the multiplier 113 into an RF signal. A demodulator 121 demodulates a signal received from the mobile station. A power control bit (PCB) extractor 123 extracts a power control bit from the output of the demodulator 121. A gain controller 125 uses the power control bit to determine the gain and supplies the gain to the multiplier 113.
In a configuration of the mobile station, a demodulator 151 demodulates a signal sent from the base station. A signal power measurer 153 measures the power of a signal output from the demodulator 151. A power control bit (PCB) generator 155 generates a power control bit from the measured power result. A power control bit multiplexer (PCB MUX) 157 multiplexes the power control bit and a pilot signal. An RF modulator 159 modulates the output of the PCB MUX 157 into an RF signal.
To control power in a mobile communication system having the above-described configuration, the mobile station multiplexes the power control bit onto a reverse pilot channel. Therefore, the mobile station transmits to the base station a reverse pilot channel signal including the multiplexed power control bit (i.e., a power control subchannel).
FIG. 2 illustrates configurations of the PCB MUX 157 shown in FIG. 1 and the power control subchannel multiplexed over the reverse pilot channel (refer to xe2x80x9cTHE CDMA 2000 RTT CANDIDATE SUBMISSIONxe2x80x9d, TR45.5, June 1998).
Referring to FIG. 2, a symbol repeater 211 spreads the power control bit output from the power control bit generator 155 to 384xc3x974 chips. A multiplexer (MUX) 213 inserts the power control bit into the fourth power control subchannel duration in a power control group indicated by a reference numeral 125.
Therefore, the pilot channel for a reverse dedicated channel, output from the PCB MUX 157, is comprised of a pilot signal having a fixed reference value and the multiplexed forward power control data as shown by the reference numeral 215 in FIG. 2. The time-multiplexed forward power control data is represented by the power control subchannel. The power control subchannel provides information about the condition of the forward link at a rate of one bit per 1.25 ms power control group (PCG). The base station controls the transmitting power of the forward link channels using this information. The power control bit is maintained at the same value during a symbol interval where one bit value is repeated through power control symbol repetition. The pilot signal is always +1 (or xe2x88x921), and the power control bit is +1 or xe2x88x921. The reverse pilot channel over which the power control subchannel is multiplexed shows that one power control group is divided into 4 power control subchannel durations as shown in FIG. 2 and the power control bit is positioned at the end in time within one power control group.
FIG. 3 is a diagram illustrating a power control process on a time basis using the power control subchannel shown in FIG. 2.
If the base station transmits a signal in a power control group unit (BS Tx), the mobile station receives this signal with a slight propagation delay (MS Rx). The mobile station measures the power of the received signal, generates a power control bit, and transmits the power control bit to the base station during the next power control group (MS Tx). The base station receives a signal including the power control bit in a power control group unit (BS Rx). Upon receipt of the power control bit, the base station waits until the start point of the next power control group to control the power according to the received power control bit (APPLY PC of BS Tx). Consequently, a delay from the measurement of the transmitting power to the control thereof by the base station is nearly two power control groups (MEASUREMENT-TO-CONTROL DELAY). Therefore, the conventional power control method has a disadvantage in that a time for controlling the transmitting power of the forward link is delayed by the structure of the power control subchannel in which the power control bit is inserted into the last (i.e., fourth) power control subchannel duration of the power control group as illustrated by the reference numeral 215 in FIG. 2.
An object of the present invention is to provide a method wherein a mobile station can transmit a power control bit so as to minimize a delay while a base station controls forward transmitting power in a mobile communication system.
Another object of the present invention is to provide a method wherein a mobile station can multiplex a power control bit multiplexed onto a reverse pilot channel at the inner part of a power control group duration in a CDMA mobile communication system.
To achieve the above objects, a method for transmitting a power control bit from a mobile station in a CDMA mobile communication system includes the steps of measuring a signal-to-interference ratio of a received signal, comparing the signal-to-noise ratio with a threshold value to generate a power control bit, and multiplexing the power control bit at a given duration among inner durations of a reverse pilot channel of a power control group to be transmitted next and transmitting the multiplexed power control bit to a base station.